This invention relates to a liquid crystal display element-driving circuit and more particularly to the digital circuit used in a digital display electronic timepiece.
In recent years, an electronic timepiece using liquid crystal as a display element has been developed and marketed. The electronic timepiece contains a large scale integration (abbreviated as "LSI") circuitry. The LSI circuitry includes various time data-handling circuits such as an oscillating circuit, frequency-dividing circuit, counter circuit, decoder circuit and output circuit. The output circuit supplies liquid crystal-driving pulses to the required segment electrodes of a liquid crystal display element. The output circuit has a plurality of output terminals provided in a number corresponding to that of the segment electrodes, thereby causing the liquid crystal display element to indicate a prescribed time data.
Measurement of output voltage and current from the respective segment electrodes of a liquid crystal display element was carried out by a very much complicated process with respect to a prior art output circuit, because some of the segment electrodes were operated at a high logical level "H" and the others at a low logical level "L". Consequently, said measurement failed to be finished quickly.
For example, in the measurement of high or low level output current from arbitrary terminal of a segment electrode, the potential of the terminal must be fixed to logical high or low level by proper means, because each terminal was impressed with A.C. voltage and time-consuming work were required to measure the high or low logical level current of all the terminals of the LSI circuitry for a liquid crystal display element which were provided in as large a number as about 40 to 50.
Further, the LSI circuitry of a liquid crystal display timepiece is generally operated by a cell, and is accompanied with the drawbacks that even when a crystal oscillator ceases to carry out oscillation due to a decrease in the power of the cell, a certain level of D.C. voltage continues to be impressed across the segment electrodes of a liquid crystal display element and a common segment electrode facing them; and said D.C. voltage is undesirably applied to liquid crystal sealed between both forms of electrode, thereby deteriorating the liquid crystal and shortening its effective life.